The present invention relates to a wheelspace windage cover plate for spanning between a turbine wheel bucket dovetail and an adjoining spacer in a turbine rotor and particularly relates to a windage cover plate for substantially precluding hot flow path gas ingestion into the turbine wheelspace cavity.
Wheelspace cover plates have been proposed and constructed in the past. Typically, those cover plates extend between the turbine wheel and adjoining spacer. The cover plates, however, are not typically readily removable for access into interior portions of the rotor. The attachment directly to the turbine wheel also causes maintenance problems and the joints between the adjacent cover plates have not been found particularly effective to minimize leakage of the hot gas into the wheelspace.
Wheelspace cover plates in general, however, preclude ingestion of hot gas from the hot gas flow path into the turbine wheelspace cavity which would otherwise cause damage to the turbine wheel. Removability of the cover plates for access to the wheelspace cavity becomes an issue in advanced turbine design because the wheelspace cavities house a multiplicity of tubing for conducting a cooling circuit, for example, employing steam as the cooling medium, for internal cooling of the buckets. Conventional wheelspace covers attached between the spacer and wheel are not readily removed without disassembly of the rotor. Consequently, access to the various tubings and joints which supply the cooling medium to the buckets for maintenance or repair is quite difficult. In a more general sense, the cover plates must also withstand high operating temperatures, severe accelerations, must have high cycle fatigue endurance and afford minimal hot gas leakage into the turbine wheelspace cavity.
In accordance with the present invention, there is provided a wheelspace windage cover for precluding hot flow path gas ingestion into the wheelspace cavity between the turbine wheel and spacer and which cover can be readily installed and removed for access to interior portions of the rotor. Particularly, the wheelspace cover comprises a plurality of cover plates arranged in a circumferential array between the spacer and a turbine wheel. Each cover plate has an engagement structure along an axial edge for engaging a complementary engagement structure on the spacer, i.e., the cover plate carries an arcuate projecting flange for engagement in a circumferential slot or groove on the axial face of the spacer. The opposite axial edge of the cover plate includes a radially extending wall having a recess for receiving a lug projecting axially from a bucket dovetail. A cover plate is provided at each bucket dovetail location. With the cover plate tongue engaged in the groove of the spacer and the cover plate in position, the bucket dovetail is received in the female dovetail on the turbine wheel. When the bucket dovetail is finally secured to the turbine wheel, the bucket dovetail lug projects into the recess on the cover plate, maintaining the cover plate in position.
Lap joints are formed between the end edges of adjacent cover plates. The tongues on the end edges of the cover plates alternate from cover plate to cover plate. That is, the circumferentially projecting tongues of one cover plate underlie oppositely directed circumferentially projecting tongues of the end edges of adjacent cover plates. With this arrangement of lap joints, access to the wheelspace cavity at any location about the rotor is available by removing one, or at the most, two, adjacent cover plates by first removing the associated bucket from its dovetail connection with the turbine wheel. Thus, by withdrawing the bucket dovetail lug from its associated cover plate, the cover plate may be removed, assuming the tongues at the end of the cover plate overlap the tongues of adjoining cover plates. If access to an adjacent location is required, the second cover plate adjacent the first cover plate may likewise be removed.
With this arrangement of cover plates and lap joints between circumferentially adjacent cover plates, gas leakage into the turbine wheelspace cavity is minimized. Additionally, the windage within the rotor is substantially reduced.
In a preferred embodiment according to the present invention, there is provided a cover plate for disposition in the space between a turbine rotor wheel and a spacer rotatable about an axis wherein the wheel has circumferentially spaced buckets, including bucket dovetails with dovetail lugs extending axially in one direction and the spacer includes a circumferentially extending groove in general spaced registration with the lugs, comprising a cover plate body having along one side an axially extending tongue for engaging in the groove of the spacer and a recess along an axially opposite side for receiving one of the axially extending lugs of the bucket dovetail and a flange projecting from each of the opposite ends of the cover plate body for engaging an adjoining cover plate about the turbine rotor.
In a further preferred embodiment according to the present invention, there is provided in a turbine rotor having a turbine rotor wheel and a spacer rotatable about an axis, the wheel having circumferentially spaced buckets, including bucket dovetails with dovetail lugs extending axially in one direction, the spacer including a circumferentially extending groove in general spaced registration with the lugs, a cover plate for disposition in the space between the wheel and the spacer and including a cover plate body having along one side an axially extending tongue engaged in the groove of the spacer and a recess along an axially opposite side for receiving one of the axially extending lugs of the bucket dovetails, the cover plate further including a flange projecting from each of the opposite ends of the cover plate body for engaging an adjoining cover plate about the turbine rotor.
In a still further preferred embodiment according to the present invention, there is provided a cover for enclosing the space between a turbine rotor wheel and a spacer rotatable about an axis wherein the wheel has circumferentially spaced buckets, including bucket dovetails with dovetail lugs extending axially in one direction and the spacer has cover engagement structure, comprising a plurality of cover plates each including a cover plate body having along a first axially facing side thereof spacer engagement structure complementary to the cover engagement structure carried by the spacer and a recess along a second axially facing side thereof for receiving one of the axially extending lugs and overlapping complementary engagement elements on registering ends of the circumferentially adjacent cover plates for minimizing fluid leakage past the cover.
Accordingly, it is a primary object of the present invention to provide a novel and improved cover for overlying the wheelspace cavity between a spacer and turbine wheel which minimizes hot gas leakage into the wheelspace cavity, while affording ease of maintenance by facilitating removal of one or more of the cover plates for access to the wheelspace cavity.